Seal Coating pavement in extreme heat can present challenges that every seal coater should be aware of.  The first should always be to the safety of the crew who is doing the application. Workers should always stay well hydrated and use the proper personal protection equipment. When the heat index is blistering up over 100⁰ it’s difficult to have compliance from a crew.  However the following PPE are required to be used, regardless of the temperature.

• Eye protection

• Particle mask to avoid inhalation hazards

• Full length clothing

• Chemical resistant boots and gloves

• High visibility vests or clothing if traffic is present

• Protective cream if applying coal tar

• Sun block 25 SPF minimum

Related: Sealcoating and Crack Repair Safety Checklist

All other safety and training procedures must also be followed as usual.

When the sun is baking down, and the pavement temperatures are over 120⁰ some unique problems can occur. Flash surface curing, tracking and power steering marks, and stickiness top the list. Allow me to offer you some help with these issues.

Flash surface curing occurs when the pavement temperature is so hot, that the sealer dries almost as soon as it touches the surface.  At first, this would seem to be a good thing, the faster it dries the faster the lot can be striped and reopened. However this flash drying has a hidden problem that many seal coaters struggle with. Even though the sealcoat is applied in what appears to be a very thin film, what happens many times in extreme heat, is that the heated pavement surface will dry the sealer so fast, that it cannot penetrate, fill the pores of the pavement, and adhere properly. The top of the sealcoat can flash dry from the heat of the sun. This will form a micro thin film on the top of the sealcoat and literally trap a micro thin layer of soft damp uncured sealcoat in between.  This soft uncured layer traps the moisture and prevents the needed evaporation. What appears to be a beautiful dry lot is allowed to open up to traffic. Unfortunately, it’s not hard enough to withstand the tight turning of a car pulling in and out of the parking space. This uncured layer, coupled with the poorly adhered flash dried bottom of the sealcoat will cause tracking and power steering marks. In extreme cases, the tires can literally pull the sealcoat right back down to the pavement.

There are three cures for this phenomena that work well. I’ll give them to you in a good, better and best order. Always apply according to manufacturer’s specification. I don’t consider this a cure because you should be doing this anyway. However I do want to point out that every manufacturer that I know of specifies an aggregate in their sealcoat, and this is not just for slip hazard. The aggregate speeds the drying of the sealer, curing, and prolongs wear-ability.

A good cure for flash drying is to always apply sealcoat in two coats. The first coat (when spraying) should me a light fog coat, a light primer if you will, just enough to barely cover the pavement. This will slightly drop the pavement temperature and give the finish coat something to better adhere too.

A better solution (the necessary one if you are using squeegee application) is to fog the pavement with a mist of water – being careful to not cause any puddles. This will accomplish two things, it will lower the pavement temperature and also allow the sealcoat to thin out just a bit, so it can penetrate down into the pores of the pavement and greatly improve adherence.

The best solution and unfortunately the most difficult for most contractors, is to thin the sealcoat that you are going to be applying with a 50/50 water sealer mixture, preferably without aggregate. This application is only for the first coat. By applying this thinned out material at a normal application rate on extremely hot days, allows the sealcoat to soak down into the pavement pores and actually give the best protection for the pavement. The finish coat will adhere well to that primer coat and you will have a fantastic result. The downside is that most contractors only work out of one tank, making this procedure complicated.

Tracking and power steering marks are a common complaint in our industry. Common causes are:

• Opening the lot before the sealer is cured

• Flash drying

• Lack of the proper amount of aggregate

• One thick coat application of sealer

The first three have been addressed, so I’d like to deal with the contractor’s who tell customers “I use one thick coat of sealer.” In the sealcoat industry, thicker is not always better, especially when it’s one thick coat. One thick coat will greatly extend the curing time of the sealcoat, this just invites flash drying issues. Parking lots get opened too soon because the sealcoat is not cured, and you’ll have stickiness, tracking, and power steering marks.

One thick coat also invites “Mud cracking.” When a mud puddle dries out, you’ll see the ground all cracked. That comes from shrinkage that occurs when water evaporates out of almost any material. When the moisture evaporates out of a thick coating of sealer it will crack just like that. Extreme heat conditions will multiply that effect because it is drying so quickly. Two thin coats will prevent many problems.

The last issue that I’d like to address is stickiness. Stickiness is normally attributed to curing time. A lot may seem to be dry, but it’s not cured or hard yet. You can walk across the lot and everything looks and feels great. It’s been in the 90⁰s and hot, everything is great! Not so fast – a major portion of our great country has high humidity and high dew points when it’s hot out. In order to cure, sealer needs all of the moisture to evaporate out of it. When the humidity is in the 80% and 90% range or the dew point is 75⁰ and the low at night is near 75⁰, your sealer is unable to dry and cure. There is nowhere for the moisture to evaporate too. Many contractors seal at night so businesses can open during the day. If the dew point and the temperature are within 5⁰ of each other, the sealer cannot dry and cure. Now you have a sticky parking lot. The contractor who tries to skip two thin coats by putting down one thick coat is really asking for problems in hot humid conditions. The easiest way to prevent stickiness issues are:

• Always follow manufacturers specifications on coverage rates

• Use the recommended amount of aggregate

• Be aware of humidity and know that high humidity will slow curing time

• Don’t seal at dusk, or at night if dew point is predicted within 5⁰ of low temperature

• Keep the lot closed until you can no longer scuff the sealcoat with your heel

These simple tips will greatly reduce problems and keep your customers smiling and coming back to you for all of their seal coating needs.

You can check the Application Temperature Cheat Sheet for crack filling, sealcoating, and line striping.

Article by Brian Coles, Sealmaster